I KNOW SOMEONE WILL BE ABLE TO ANSWER THIS QUESTION. WHICH IS WHEN CHANGEING SPARK PLUGS DO YOU HAVE TO USE HARLEY BRAND?

 

NGK, ACCELL ,DENSO ,and Autolite are good ones.

 

I have tried them all and found the stock HD plug works best, and has the smoothest idle.

Steve

 

personally Harley-Davidson sparkplugs worked fine for the most part, for a stock engine. But, if that's not the case you need to expand parameters! I personally now use Autolite, after recommendations by my tuner. I was having some difficulties with stock plugs, and moderate RPM roll on's. So far I've seem to cure the problem with the change. I find them to burn exceptionally clean, virtually no carbon buildup on cold engine starts like I did with the Harley-Davidson plugs. Also after a good days hard ride I find porcelains, to be exceptionally clean and residue free.

 

Stock Harley plugs here, no complaints and great idle.

 

Autolite 4164's

 

+1 every 10K

 

I just changed mine and used the Harley plugs. I'll spend the $6 dollars at the local dealerfor the peace of mind. I'm not sayingyou have to use the Harley plugs but the service manual says "no substitutes". GoodLuck

 

Stock HD or NGK. Mostly NGK now as i like how i can read the a bit better....They been great on stock bikes and some of the larger builds i have been doing.

 

At my last shop we used stock 6R12's on all kinds of motor combos up to mid 130 HP. Anything that had a lot of compression got 10R12 V-Rod plugs including a 147 HP 131" build. Seen EVERY other brand of plug cause problems